A quartz oscillator which is used for a quartz oscillation generator, a gyro-sensor, or the like, is conventionally manufactured using a method comprising the steps of cutting out a quartz piece of desired shape from a quartz substrate, forming electrodes for generating oscillation of the quartz piece, and mounting the quartz piece having electrodes formed thereon in a packaging container. As the oscillation frequency of a quartz oscillator depends to a large extent upon the external geometry of the quartz piece, the step of cutting out the quartz piece from the quartz substrate is an important step in determining the performance of the quartz oscillator.
Either a cutting process or an etching process has been conventionally employed in order to cut out quartz pieces from quartz substrates. In particular, as an etching process, in which the quartz substrate is chemically dissolved and processed, permits fine and precise processing to be performed, it is frequently used in the manufacture of miniature quartz oscillators.
An example of the method for manufacturing quartz pieces by means of an etching process is shown in FIG. 6 (see, Patent Reference 1 and Patent Reference 2). First, as shown in FIG. 6(a), masking layers 21 and 22 having light interruption capability are respectively formed on both sides of a quartz substrate 10, and a resist layer 31 of photosensitive material is formed on the masking layer 21 and a resist layer 32 of photosensitive material is formed on the masking layer 22.
Then, as shown in FIG. 6(b), exposure masks 11 and 12 are disposed in parallel to the quartz substrate 10, and exposure to light is performed from both sides of the substrate 10 such that predetermined portions of the resist layers 31 and 32 are exposed to light.
Next, using a special developing solution, the resist layers 31 and 32 are developed to form patterned resist layers 33 and 34 as shown in FIG. 6(c). Then, using the resist layers 33 and 34 as masks, the portion of the masking layers 21 and 22 which has no resist layers 33 and 34 formed is removed by dissolution with the etching solution. Patterned masking layers 23 and 24 as shown in FIG. 6(d) are thereby formed.
Then, as shown in FIG. 6(e), the quartz substrate 10 is subjected to etching by using the resist layer 33 and masking layer 23, and the resist layer 34 and masking layer 24, as masks, respectively, to cut out quartz pieces 15. Finally, as shown in FIG. 6(f), the resist layers 33 and 34, and the masking layers 23 and 24, are removed to obtain the quartz pieces 15.
Another example of conventional processing methods for processing quartz pieces by means of etching process is shown in FIG. 7 (see Patent Reference 3). First, as shown in FIG. 7(a), transparent films 41 and 42 are respectively formed on both sides of a quartz substrate 10, and a resist layer 31 of photosensitive material is formed on the transparent film 41 and a resist layer 32 of photosensitive material is formed on the transparent film 42.
Then, as shown in FIG. 7(b), a exposure mask 13 is disposed in parallel to the quartz substrate 10, and light exposure is performed from one direction to expose predetermined portions of the resist layer 31 and 32 to light.
Next, using a special developing solution, the resist layers 31 and 32 are developed to form patterned resist layers 33 and 34 as shown in FIG. 7(c). Then, using the resist layers 33 and 34 as masks, the portion of the transparent film 41 and 42 which has no resist layers 33 and 34 formed is removed by dissolution with the etching solution. Patterned transparent films 43 and 44, as shown in FIG. 7(d), are thereby formed.
Then, as shown in FIG. 7(e), the quartz substrate 10 is subjected to etching by using the resist layer 33 and transparent film 43, and the resist layer 34 and transparent film 44, as masks, respectively, to cut out quartz pieces 16. Finally, as shown in FIG. 7(f), the resist layers 33 and 34, and the transparent films 43 and 44, are removed to obtain the quartz pieces 16.    Patent Reference 1: Japanese Patent Unexamined Publication No. S56-106412 (page 4, FIG. 1)    Patent Reference 2: Japanese Patent Unexamined Publication No. H11-199400 (page 1, FIG. 6)    Patent Reference 3: Japanese Patent Unexamined Publication No. H10-270967 (page 1, FIG. 3).
In the conventional etching process for processing quartz pieces as shown in FIG. 6, in order to obtain a quartz piece 15 which is symmetric with respect to the up and down direction (in the Figure), it is necessary to precisely position the patterns in the exposure masks 11 and 12 in the step shown in FIG. 6(b). For this purpose, it has been usual practice to provide an optical system that permits simultaneous observation of the upper and the lower surfaces (in the Figure) of the quartz substrate 10, and positioning of the exposure masks 11 and 12 is performed using a microscope with magnification of 10×–100×.
In order to be able to observe the position of the exposure masks 11 and 12 accurately, it is generally more desirable to use a microscope with high magnification (about 100×) than that with low magnification (about 10×). However, when a microscope with high magnification is used, it is difficult to focus at the same time on the exposure mask 11 and the exposure mask 12 which are disposed on opposing sides of the quartz substrate 10. Therefore, in the conventional method, irrespective of any attempt to position the exposure masks accurately, the positioning of the exposure mask 11 and 12 inevitably gives rise to shift (s) of about a few μm.
The shift (s) as shown in FIG. 6(b) leads finally to a quartz piece 15 having a distorted cross sectional shape as shown in FIG. 6(f). The quartz piece 15 having such a distorted cross sectional shape does not oscillate as designed. As a result, a quartz oscillator using such a quartz piece 15 does not have the design oscillation frequency and precision.
In addition, the shift (s) as shown in FIG. 6(b) is not constant in magnitude, but is variable in the order of at least a few μm. Therefore, the geometrical shapes of the quartz pieces 15 to be processed are not constant, but vary in the range of a few μm. As the oscillation frequencies of quartz oscillators depend upon the external geometry of the quartz pieces 15, the oscillation frequencies of the quartz oscillators manufactured from the variable quartz pieces 15 are also variable. As the oscillation frequencies of individual quartz oscillators is variable, product reliability is degraded.
In the method for processing a quartz piece using the conventional etching process as shown in FIG. 7, no centering of two exposure masks needs to be performed. However, as light transmission of the quartz substrate 10 is less than 100% (93–95%), light for exposing from one direction is attenuated and diffuses upon passage through the quartz substrate 10, and the light intensity for irradiating the resist 31 is reduced. As a result, the size of the portion of the resist 31 which is removed in the step of FIG. 7(c) is reduced so that the width of the pattern 33 is wider than the width of the pattern 34 by (r) (1–2 μm).
The difference (r) in FIG. 7(c) leads finally to formation of a quartz piece 16 having distorted cross sectional shape as shown in FIG. 7(f). The quartz piece 16 having such distorted cross sectional shape does not oscillate as designed and, consequently, a quartz oscillator manufactured by using the quartz piece 16 does not have the designed oscillation frequency and precision.
In addition, the difference (r) in FIG. 7(c) is not constant, but occurs in variable amounts. Therefore, the geometrical shapes of the processed quartz pieces 16 are not constant, but vary within a predetermined range. As the oscillation frequency of quartz oscillators depends upon the external geometry of the quartz pieces, the oscillation frequencies of the quartz oscillators manufactured from the variable quartz pieces 16 are also variable. As the oscillation frequencies of individual quartz oscillators are variable, product reliability is degraded.